But I still want to use _insert testing library_

Karma is not a testing framework, nor an assertion library.
Karma just launches an HTTP server, and generates the test runner HTML file you probably already know from your favourite testing framework.
So for testing purposes you can use pretty much anything you like. There are already plugins for most of the common testing frameworks:

Installation.

Using it.

This is so great. I want to help.

Why did you create this?

Throughout the development of AngularJS, we've been using JSTD for
testing. I really think that JSTD is a great idea. Unfortunately, we
had many problems with JSTD, so we decided to write our own test
runner based on the same idea. We wanted a simple tool just for
executing JavaScript tests that is both stable and fast. That's why we
use the awesome Socket.io library and Node.js.